The objective of our cancer program is to understand the mechanisms of growth control of normal and malignant cells. The program is organized in four parts: 1) Tumor virology: These studies are aimed at understanding the genetic organization of RNA and DNA tumor viruses and the effects of viral gene expression on cell growth regulation. The objective is to define the nature and control of molecules that affect cell growth regulation. 2) Cell surface immunology and biochemistry: We are using immunological, biochemical and genetic techniques to study the nature, function and regulation of selected molecules on normal and malignant lymphocytes. These studies are aimed at understanding how surface molecules in general, and tumor-associated molecules in particular, are controlled, and at understanding the properties of cells of the immune system whose function it is to recognize and kill tumor cells. 3) Mammary cell growth control and breast cancer: This is a new aspect of the program which will be developed by Dr. Renato Dulbecco. He and his colleagues will study the differentiation of the mammary gland in rats and mice, the growth control of mammary epithelial cells, mechanisms of carcinogenesis and properties of mammary cancer cells. The objective is to develop approaches toward prevention and treatment of breast cancer. 4) Differentiation and cell growth control: This part of the program has developed from studies carried out so far. We plan to study the relationship of cell differentiation to viral gene expression and cell growth control, mechanisms of hormone action, and differentiated functions in tumor cells. The objective is to develop new approaches toward controlling the growth of tumor cells.